ИСТИНА

We present the first observation of terahertz (THz) wave generation by photo-excitation of a liquefied gas - liquid nitrogen (LN). We use double pulse excitation scheme and apply both "single-color" and "dual-color" regimes of LN excitation with high power femtosecond laser pulses. Our experimental results show clearly that under acting of femtosecond laser radiation liquid and air emit THz waves in a very different way. Careful theoretical examination of the results shows that both the ionization of the medium and its nonlinear susceptibility play a considerable role in the generation of THz radiation in LN. We assume that the mobility of ions and electrons in liquid can play an essential role in the THz generation by acting through a quasi-static electric field formed by means of ambipolar diffusion mechanism.